“Microfinishing” or “superfinishing”, as it is known in the art, is a surface finishing process wherein a grinding means is brought to bear against a workpiece which has been previously rough ground. Microfinishing is a low velocity abrading process which generally follows rough grinding. Because microfinishing incorporates lower cutting speeds than grinding, heat and pressure variants may be minimized to provide improved size and geometry control. Those skilled in the art recognize that surface quality or roughness is measured in roughness average values (Ra) wherein Ra is the arithmetical average deviation of minute surface irregularities from hypothetical perfect surfaces. Microfinishing can provide surface quality of approximately 1 to 10 μin. (0.025 to 0.25 μm). Bearing surfaces of crankshafts, cam shafts, power transmission shafts in similar machine components that rotate on journal bearing surfaces generally require this surface finish for satisfactory operation.
Conventional mass production microfinishing machines have the ability to finish all the bearing surfaces on a workpiece in one operation. These machines contain a plurality of abrasive tape segments which are aligned with respect to the bearing surfaces. In operation, the workpieces are rotated as the microfinishing machine causes abrasive tape segments to contact and thus finish the bearing surfaces. These large multi-abrading machines are capable of successive steps in one operation including rough grinding, grinding and microfinishing.
As is common in large scale production, failures may occur at one or more of the grinding areas or abrasive tape positions. As a result, workpieces may be produced with one or more bearing surfaces (but less than all bearing surfaces) which are not finished to the required surface quality specifications. In such cases, the grinding machine operator must then remove and scrap the defective workpiece. Because microfinishing is the final stage in surface treatment operations, i.e. after rough grinding and grinding, the scrapping of microfinished parts results in a substantial loss of both material and labor to the machinist.
Microfinishing processes are used in automotive applications in the manufacture, repair and rebuilding of internal combustion (IC) engines. Such engines not only require finely finished bearing surfaces for engine efficiency, but also for increased durability and longevity. In the initial manufacturing stage, crankshaft and camshaft bearing surfaces are microfinished to particular roughness specifications by previously mentioned, conventional mass production microfinishing machines.
In the repair or rebuilding stages, engine components such as crankshafts and cam shafts from faulty engines or older engines, are removed and reground to remove ten to thirty-thousandths of an inch of stock from the existing bearing surfaces. The bearing surfaces of these components are then polished or microfinished by placing the respective workpieces on a lathe and manually bringing a microfinishing material in contact with the rotating bearing surfaces. This microfinishing material is often a section of abrasive material mounted on a support correspondingly shaped to the bearing surface. It is generally recognized in the industry that these manual finishing operations are inadequate for achieving finished surfaces of standard quality.
Automotive repair and rebuilding operations reclaim and refinish workpieces from hundreds of various internal combustion engines with different designs. New and small engine crankshafts, remanufactured crankshafts, high performance crankshafts and diesel crankshafts also may require special finishing. Programmably controlling a finishing machine to accept each individual workpiece that requires microfinishing from different internal combustion engines is uneconomical and inefficient.